Our past studies have indicated that alcohol abuse leads to a loss of docosahexaenoate (DHA), the major polyunsaturate in the nervous system. These losses contribute to deficits in dopaminergic neurotransmission and likely to excesses in CRH neurotransmission which are characteristic of states of chronic addiction. Nutritional inadequacies, particularly during early development, may also lead to such losses in this essential fatty acid. Residual developmental deficits include lower IQ, risk for ADHD and conduct disorders. This phenotypic profile is characteristic of an adverse developmental trajectory towards increased risk of substance abuse. However, tissue deficits of omega-3 highly unsaturated fats (n-3 HUFAs) may also be caused by excess dietary intakes of omega-6 fats, in particular linoleic acid. In a portfolio of animal and human trials, we have evaluated the effects of lowering dietary intakes of the omega-6 fatty acid linoleic acid on elevating endogenous production of the long chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid. During the 20th century dietary intakes of omega-6 fats increased dramatically. Linoleic acid increased from approximately 1 % of energy to more than 8 % of energy. We modeled these changes in animal studies and found that lowering linoleic acid intakes reduced excessive levels of endogenous cannabinoid like molecules. Reducing the linoleic acid intake reversed obesity, despite animals consuming a high fat diet (60 %en) and was able to induce obesity even in low fat diets (212% en). This study provides a critical framework for reducing excessive endocannabinoid activity by reducing dietary intake of their precursor molecules. Thus, lowering the omega-6 fatty acid linoleic acid, is being evaluated in three human clinical trials. 1)Among subjects with chronic daily headache, selective lowering of linoleic acid, and linoleic acid lowering in conjunction with elevating EPA and DHA intakes, reduced arachidonic acid in phospholipids and elevated EPA and DHA in serum. These changes caused a 50% reduction in headache severity and duration. 2) The Optimal Omega-3 trial is a collaboration with the DOD nutrition directorate, USARIEM. First we have translated the principle of linoleic lowering to the production of poultry meat (and eggs) enriched in omega-3 fats with significantly reduced omega-6 fats. These highly enriched food stuffs will replace standard commodity foods in recipes used in the US garrison food lines. 3) A third human protocol is active within the NIH Clinical Center to evaluate the effects of selective linoleic acid lowering on reducing adiposity among overweight women. The protocolwill selectively lowering intake to approximately 1 en%. These dietary changes are expected to reduce excessive endocannabinoid levels, improve satiety and results in weight and adipose loss. Elongation and desaturation of the omega-3 alpha linolenic acid (d5) to EPA and DHA will be quantified using steady state infusion and GC- MS/MS/MS quantification. Since linoleic acid is a polyunsaturated fat, it has been critical to determine if advice to reduce intake might be harmful or beneficial. The American Heart Association has specifically advised consumption of at least 5 to 10% of energy as omega-6 PUFAs substantially based on randomized controlled trials (RCTs) of mixed n-3/n-6 PUFAs and meta-analyses of their CHD outcomes. To better evaluate these studies we: conducted an extensive literature search and performed a meta-analysis. For non-fatal myocardial infarction (MI) + CHD death, the pooled risk reduction for mixed n-3/n-6 PUFA diets was 22% (RR=0.78 95%CI 0.65-0.93), compared to an increased risk of 13% for n-6 specific PUFA diets (RR=1.13 95%CI 0.84-1.53). Risk of non-fatal MI + CHD death was significantly higher in n-6 specific PUFA compared to mixed n-3/n-6 diets (Q-statistic=5.44, df =1, p=0.02). RCTs that substituted n-6 PUFAs for trans and saturated fatty acids without simultaneously increasing n-3 PUFAs produced an increase in risk of death that approached statistical significance (RR=1.16 95%CI 0.95-1.42). We found that advice to specifically increase n-6 PUFA intake, based on mixed n-3/n-6 RCT data, is likely to increase CHD risk. The Sydney Diet Heart Study, conducted from 1966-1973 was unique as it was an intervention specifically with the n-6 polyunsaturated fat linoleic acid (LA) in place of saturated fats. Careful evaluation of recovered data from the Sydney Diet Heart Study show no indication of cardiovascular benefit from elevating dietary intake of LA above 6 en%. By contrast, there was a significant increased risk of death from coronary heart disease and all-cause mortality in the Sydney Diet Heart Study. Thus, from the available RCT data, increasing LA intakes above 6 en% appears likely to increase the risk of coronary heart disease and death. A separate but related line of investigation has been to evaluate the impact of genetic variants in the metabolism of essential fatty cid precursors to their highly unsaturated products. Genetic variants in the FADS 1-2 gene complex are thought to influence the ability to desaturate 18 carbon fats, ALA and LA to their respective products AA and EPA/DHA. A study by Caspi et al has suggested that rs174575 within the FADS2 gene moderates this effect so that children homozygous in the minor allele (GG genotype) have similar IQs irrespective of breast or feeding method. Breast milk contains preformed DHA whereas infant formula did not. In our study of 5934 children aged 8 years, an interaction with this polymorphism was observed such that breastfed GG children performed better than their formula fed counterparts by an additional 5.8 points 1.4, 10.1 (interaction p 0.0091). Interaction results were attenuated by about 10% after adjustment for 7 factors. We evaluated data from blood samples for 4342 pregnant women, 3343 umbilical cords reflecting the newborns blood supply and 5240 children aged 7 years to investigate the associations of polyunsaturated fatty acids with rs1535 and rs174575 two polymorphisms in the FADS2 gene. We compared the effect of two polymorphisms in the FADS2 gene on fatty acid profiles at three time points: during pregnancy for the mother, at birth for the neonate and at 7 years old for the child. In all three datasets, the two genetic variants had strong associations with most of the polyunsaturated FAs reported in this study. These results were consistent with the minor allele being associated with lower activity leading to reduced amounts of the products but increased amounts of the unmetabolised precursors. In this population we also investigated associations between erythrocyte maternal fatty acids in pregnancy and child IQ at 8y amongst 2839 mother-child pairs. The strongest association was comparing the highest quartile of osbond acid (22:5n-6) and lower verbal IQ, -2.26 points 95% CI -3.72, -0.8; p<0.003 and the lowest quartile of DHA (22:6n-3) with lower full scale IQ, -1.6 points 95% CI -3.0, -0.1; p<0.033. using linear regression. These findings are consistent with the interpretation that during DHA insufficiency, with reciprocal replacement with osbond acid is suboptimal for neural development.